Metamorphosis
by skygirl55
Summary: An unprecedented viral outbreak alters the course of Richard Castle's life forever. AU-Post-To Love and Die in LA. Caskett.
1. Chapter 1

_An unprecedented viral outbreak alters the course of Richard Castle's life forever. AU-Post-To Love and Die in LA. Caskett._

* * *

 **A/N:** This does toe the line of 'sci fi' so if you're not interested in that I understand.

* * *

The streets were silent; eerily silent.

This was New York City, for god's sake; honking horns, squealing brakes, and the hum of traffic were virtually a constant presence, but not that day. Not the day before, either. Not for…well, it was going on three weeks now, wasn't it? Three weeks; three weeks was all it had taken for his world to change irreversibly.

Richard Castle stepped up to the edge of the sidewalk in front of his building and scanned the streets for an available cab. The citywide ban on public transportation had been lifted just two days earlier, so the cabbies should have been back at it—trying to make up for two weeks' worth of lost wages—but there wasn't a yellow car in sight. He couldn't say he was shocked, but that did present him with a conundrum. The subways still weren't running, and it was too far to walk to the Twelfth. He briefly considered walking the handful of blocks to Bloomingdales, thinking there would be a cab or two waiting there, but then he realized that a department store would probably be one of the least visited locations these days. Sighing to himself, he made a one-eighty and walked back towards the apartment building so he could get his car keys.

Eight minutes later, Castle eased his Mercedes out of the entrance to his building's underground garage. Without much traffic, he was able to pull out onto Broome Street smoothly and then turn up Lafayette so he could make his way uptown. Block after block he drove, seeing hardly more than a few dozen cars and only stopping for traffic lights. Since when were the streets not gridlocked on a weekday late in the afternoon? The hairs on the back of Castle's neck stood up as he saw a handful of individuals making their way down the sidewalk—men; only men. It was so strange; had it be any other day he would not have thought much of it, but in that moment he wondered just how long it would be before he passed a female on the street.

As a mystery writer with a poorly hidden flair for drama, he had envisioned countless s scenarios in his mind over the years. Some had made it to paper; some had not. Of those that had not, the vast majority were of the murderous kind. Some were simply implausible; some skirted the edge of potentially realistic, but continually escaped his grasp when it came down to hammering in that last plot detail to make the scenes mesh together. Still others were shelved because they were simply too gruesome to imagine or describe to his readers.

Of those scenarios not murder related, many of them strayed into the genre of post-apocalyptic. As a practicing enthusiast for zombie apocalypses, the vast majority included the undead in some way, shape, or form. What lay in among rotting corpses come to life involved nuclear holocausts, asteroids crashing into the earth, and, of course, an alien invasion or two.

In his forty years of imagining scenarios, Richard Castle had never come up with one as close to the reality he faced presently in the wonderful city of New York. He doubted anyone could have predicted this. Not even the most twisted of minds. Had he pitched such a scenario to one of his publishers he was certain they would have impolitely rolled their eyes and called him a crazy person. "No one will read a book like that, Mr. Castle; it just doesn't make any sense." He imagined they would have said something similar. Yet, there he sat, in a world forever changed.

The nightmare had started just three weeks prior. On a Friday, just a week after returning from L.A. with Kate, Castle decided that he needed a long weekend in the Hamptons. He bid goodbye to his mother and daughter under the guise of needing to visit the home they hadn't been to in several months and make sure it was ready for the upcoming summer, but that reason was secondary. Simply put: he needed a break.

In some ways, his journey west with the lovely detective had strengthened their partnership. By speaking to him about Royce the way she had, Kate had opened up to him more than ever before and that was a good thing; there was no doubt about that. They'd also had a moment in their hotel suite—a moment that, while heart-stoppingly lovely, had also failed to become more, just like all the others. Castle wanted more—god, did he want more—which was why returning to the precinct two days earlier to see Kate hugging her doctor boyfriend goodbye stung with extra force.

Castle couldn't understand it—he truly couldn't. Was Josh a good man? Probably; Castle didn't know him well enough to appropriately judge. He was a doctor who did charitable work so he certainly wasn't a _bad_ guy, but he also wasn't the right man for Kate; Castle knew that deep within his soul. He was the better man for her—he was! And, yes, his opinion was far from objective but he knew—that moment they'd had in the hotel suite solidified it even more in his mind. He knew he was the best man possible for her, yet she didn't see it—or couldn't. He was deeply entrenched into the "just partners" position and, at that particular moment, he was too deeply in love with her to care, but that didn't mean her intimate moments with Josh didn't chip away at his heart each and every time he witnessed them.

Deciding a break would be the best thing to clear his head, Castle had made his Hamptons plan and embarked on the several hour journey just after grabbing an early lunch. For the first half hour he listened to talk radio, and briefly heard a news report about a flu outbreak striking the city, which seemed particularly odd given how close it was to summer, but he didn't think much of it, changed the station, and finished out his drive listening only to music.

Saturday morning after a long walk on the beach, he turned on the TV while making his brunch. Once again there was a report about the flu outbreak, that time stating that the CDC was investigating, because it appeared as though the flu virus was affecting mostly women. When he heard this, Castle gave his television a peculiar look. He'd never before heard of a flu virus—or, really, any virus—being gender specific and he wondered at that time if the reporter had made an error.

Castle was so dismissive of the bizarre report that he never even thought to call his mother or daughter to check in; he simply continued on with his day: checking on their pool chemical supply, throwing sheets in the laundry to freshen them up, and trying to think his way through the next case Nikki and Rook would face. It wasn't until dinner time that he booted up his laptop and checked his social media accounts; only then did he become alarmed.

Boston, Chicago, Seattle, and Los Angeles in addition to the Big Apple were all trending—all seemingly suffering from the inexplicable women-only flu outbreak. Equally confused and intrigued, Castle began searching the hashtags and looking for posts and articles that would give the real story—not the glamorized media version. He soon learned that hospitals in all five major cities were being overrun with patients suffering from high fevers, nausea and vomiting. Other posts were encouraging everyone to stay home and wear masks if they needed to be out in public, for tens of thousands seemed to be getting sick overnight.

After an hour of reading bleaker and bleaker tales, Castle phoned his daughter to see if she'd heard about the outbreak. Evidently, Alexis had spent nearly the entire day studying for her exams and only ventured out for dinner a few hours earlier. At that time, she'd seen an atypical amount of people on the subway wearing masks, and asked her friend what was going on; that was the first she heard of the virus. Castle told his daughter to stay in for the rest of the weekend and went to bed that night only moderately concerned about the illness. By the next morning, everything had changed.

Even three weeks later the knowledge they had was inconclusive. Bio-Terrorism was the term being floated by the media outlets and it seemed as appropriate as anything, though the perpetrators had yet to be found. The CDC had no official comment on the outbreak other than it was categorized as being "under control," so most of the raw information came from the internet; that's where the true horrors of what happened could be found.

Not one single man had come down with what had been dubbed the XX Plague. Of all the cities hit, the women of New York, Boston, and Chicago had been hit the hardest. Some sites estimated over sixty percent had been infected, others said upwards of eighty. The disease, they believed, was airborne—that explained how it spread like wildfire through each metropolitan area—and one of the most severe and fast-acting cases of the flu that had ever been reported.

As unsettling as those factors were, they were not the most terrifying. Within one week it became evident that it didn't seem to matter much whether the woman was young, old, healthy or chronically ill; the XX Plague didn't discriminate with its eighty percent mortality rate—the highest in modern history with the exception of Ebola. Worse yet, the disease struck quickly, with most patients succumbing within seventy-two hours of the fever's onset.

Of course, at the time, Castle did not know any of that. He merely arrived home late Sunday night to find his mother in bed, her temperature well above one hundred, and his daughter dutifully tending to her, though her complexion grew paler by the hour. Come morning, neither woman was able to move from bed. The writer tried to call for an ambulance, but by that time the hospitals had been restricted on how many patients they could take in. Several hours of phone calls and fifty thousand dollars later he'd procured a private doctor from Philadelphia who hooked his family members up to IV fluids and sadly informed him that nothing could be done; the virus was too new and did not appear to be responding to any treatments.

Later that day, after making sure his mother and Alexis has as much clear chicken broth as they could drink, Castle thought for the first time to call Ryan, thinking the police would have to know more than him. Their conversation was brief and he learned that no, they did not know anything; they were just as confused—and panicked. Many of the female officers had fallen ill, but Montgomery had forced Kate into a make-shift quarantine so she was, to that point, not ill.

 _Kate_.

It stood to reason that only the grave illness of his mother and daughter would push the detective from Castle's mind. Other than the duo of red-heads, she was far and above the most important person in his life—even if she didn't feel the same. The fact that she remained well gave him hope, but unfortunately that feeling didn't last.

The next several days were mostly a blur for Castle. His mother passed sometime overnight on Tuesday, which, while devastating, Castle hardly had an opportunity to process since he threw his entire focus to Alexis in the hopes of keeping her alive. When she made it to Thursday morning and her fever had ticked down to 100.5, he really thought she was in the clear, but that afternoon her breathing became labored, she had a seizure, and took her final breath with his arms still around her.

That moment had been Castle's breaking point. No parent should ever have to bury their child and for him he'd lost both mother and daughter in less than two days. He was certain the physical pain pounding out of his heart and coursing through his body would end his life as well, but it never did. Still, everything was a chore: standing up, taking a step, taking a drink.

For a week straight he went to bed, slept ten hours, not really caring if he woke up, and then he'd get up and move to the couch, where he'd stare blankly off into space for another ten hours. On the rare occasion he did shuffle into the kitchen, he did so out of pure habit, for he knew the emptiness that filled his gut was in no way related to actual hunger.

A week after Alexis's death, when the remains of his loved ones were returned to him in ornate urns (due to the high volume of deaths and the unknown nature of the virus, cremation had been the only available option) Castle attempted to pull himself from his stupor. He showered, went to the corner bodega and retrieved milk and eggs to make himself a proper meal, and then sat down at his laptop. He tried to bring himself to care about his writing work, but couldn't; odds were Gina and Paula would never again nag him for chapters. Instead, he surfed the web, reading progressively more tragic tales of the millions of women that had passed away.

 _Millions_.

That figure was staggering—and talking about New York City alone! Though the bizarre illness seemed mostly isolated in those five cities, the death tolls were still being calculated. Perhaps the only positive news was the report that new outbreaks were almost down to zero. Just as Castle was seriously contemplating cracking open yet another bottle of scotch, a calendar reminder popped up on his computer screen with a chime.

The writer had dozens of them programmed, some months in advance. Mostly they were chapter due date reminders (lord knows he needed those) but some were little anecdotes; comments to get him through the day—to remind him why he did what he did. This reminder was one of those. Truly, it could not have been simpler, but it was just enough kindling to relight the fire within him.

 _What would Nikki Heat do?_

What _would_ Nikki Heat do? Would she wallow in sadness? Play the 'woe is me' game? No, she wouldn't. Nikki Heat would fight. She would fight until she could fight no more. Then, somehow, she would find the strength to pick herself up and keep going.

Given his deep state of grief, this was easier said than done, but day by day he'd grown stronger, his chest felt a little bit lighter. With another few days gone he knew he was ready to venture out into the world—well, his world: the Twelfth.

Other than their phone call at the onset of the outbreak, Castle had only one communication with the team of detectives; a text message from Ryan stating that Jenny had fallen ill and he was taking leave to tend to her. That had been the day before Alexis died, and he had not really thought to contact them since. Now, so much time had passed, he felt he needed to do so in person if for no other reason to offer a hug of condolence.

As he neared the Twelfth, Castle realize just how truly perplexing it was not to see any women on the street. Had he not been acutely aware of the recent devastating virus, he wasn't sure he would have noticed it at first. Many times he had walked down a crowded Manhattan sidewalk completely surrounded by men in business suits—particularly if he was near the financial district—and never took much notice to it. The nonappearance of one gender over another had never before struck his interest; however, since he knew he would not be seeing any women, their absence was palpable.

As he searched for an available parking space outside the precinct building, the writer wondered when he would next see another woman on the streets. Based on all the news he was seeing online and on television, it seemed as though most women were being encouraged to hold up indoors, but now that the outbreak seemed to have dissipated, surely the ones that survived would be out and about. Upsetting as it was, he believed their sightings would be few and far between, and that was certainly not a concept he would easily get used to.

Stepping inside the lobby of the twelfth, Castle wasn't even questioned or stopped by the front desk clerk; the man merely nodded at him and waved him along. Absent were the usual smiled and jokes he received from the vice squad or jabs from robbery as he made his way towards the elevators. Every man he passed was stone faced and Castle couldn't really say that he blamed them.

On the homicide floor the different tone in the atmosphere was most striking. He wasn't greeted by Hastings or Karpowski; he imagined they'd both been stricken and passed weeks earlier. LT did give him a nod, but his usual grin was gone. In fact, Castle feared his trip to the Twelfth might make him sadder instead of more grounded until he neared the bullpen and spotted the male duo with whom he was most familiar. For the first time since the passing of his daughter, a half smile crossed his face and he approached.

"Good to see you." Ryan extended his hand and then pulled the writer into a one armed hug.

"You too." Castle returned. He shook Esposito's hand in turn.

"How's…how are…?" Ryan's voice drifted off at the implied question. Despite the lack of context, Castle understood and even appreciated the vague nature of the comment; there was no need to come right out and ask a question that had a fairly obvious answer.

The writer gave a brief shake of his head. "No. Both of them right after it started."

Both men offered apologies before Ryan added, "Jenny, too, and my sister."

"Feels like everyone," Esposito added. "Oh, ah, except for Lanie—she's still in the hospital, but through the worst of it so they think she'll make it."

"That's great," the writer said genuinely. Sucking in a deep breath he managed the next words without vomiting, which he considered a personal victory. "And Beckett?"

He braced himself for the answer; terrible and heart wrenching as it was, he knew. The last he'd heard, Montgomery forced her into quarantine which, in theory, should have put her in a position to avoid illness, but he also knew his partner quite well. She was not one to sit idly by and shirk her responsibilities—even at the risk of her own safety. She would have been out in the trenches with everyone else and thus he simply assumed she'd, too, fallen ill. He needed to hear it, though; he needed to hear Ryan say the words and then he would start the grieving process all over again—that was, assuming his heart was still made up of pieces large enough to break.

Ryan opened his mouth to respond, but before any words could form, the clicking of heels against the tile hallway floor answered for him. Even if Castle hadn't known about the sudden reduced female population he would have recognized that walk simply from its gate. Terror immediately took hold of him. He'd been so prepared for her illness coming face to face with her was not something he thought he could handle in that moment. Yet, when he turned his head to the left, there she was looking as jaw-droppingly gorgeous as he'd ever seen her, though she looked no different than usual in her white shirt, black blazer, and dark jeans.

"C-Castle?"

Her melodic if not slightly surprised voice hit his ears just as he turned to spot her. Instantly, his breath came out in seizing, choking splutter. He lost all control of his emotions and began weeping just a few feet from the elevator on the homicide floor of the twelfth precinct.

For a solid five seconds she merely stared at him, presumably stunned not just by his presence, but by his violent emotional outburst, but then she sprang into action.

"Castle, oh my god, Castle. Are you-? Here let's…let's go in here."

With his hands covering his face, the writer allowed the detective to guide him towards the breakroom, one of her warm hands resting gently on his mid-back and the other on his shoulder. Before he even realized what was happening she had pushed him towards the couch and, several moments later, thrust a pile of napkins into his lap as she apologized for not finding any tissues.

He spluttered out a thank you before picking up a napkin and blowing his nose in it loudly. Then, he began apologizing as she settled down beside him, their thighs nearly touching. "It's okay," she said soothingly. When he ventured a glance in her direction, she offered a smile. "I'm glad to see you too."

"Oh god, Beckett." He sniffled out. "I'm sorry, I just—I thought you were…"

She placed her hand gently on his bicep. "Oh, no Castle I'm fine; I was never sick. Montgomery forced me into the quarantine he set up, but you know me—I was like a caged animal in there. Only lasted three days before I snuck out. Course Montgomery still wouldn't let me go far, but I've been fine the whole time." She rubbed her hand over his arm before bringing it back to rest in her lap. "I tried to call you a few times last week, but it just kept going right to voicemail, so I wasn't sure if…"

"They're gone," he sniffed out. "Mother and Alexis…"

She nodded tersely as though she had been expecting it, but she returned her hand to his arm, that time giving it more of a squeeze. "I am so sorry. I cannot even imagine what you're going through right now."

"'s not just me," he mumbled out. "So many people…news said the fatality rates are seventy percent…"

"It's more like ninety." She commented, though it was half-under her breath. When his red-rimmed eyes widened, she bobbed her head. "Ninety percent fatality rate with less than one percent being immune all together."

Ninety percent fatality rate—well, as horrifying as that was, it did make him feel ever so slightly better about the passing of his mother and Alexis; they truly had not really had a chance to survive. Yet, the more interesting point was her comment about immunity. Surely if Beckett had, as he assumed, refused her quarantine and helped her colleagues, she would have been exposed, which mean he could only assume she felt into the latter category. "Are you…?"

She bobbed her head. "I don't know for certain, but I think so yeah. I mean, I found one of the vice cops passed out in the bathroom just before Montgomery quarantined me. She ended up dying and I never had so much as a fever, so that's the theory we're operating on."

Reaching for another napkin to blot his cheeks, Castle said without thinking, "I always knew you were one in a million."

Kate laughed and bumped her shoulder against his before saying his name warningly. When he felt her body collide against his, Castle's chest felt lighter than it had in almost a month and a new wave of emotion filtered through his body. Kate was alive—she was okay. The world that had seemed so bleak not fourteen days earlier was suddenly shining with an unexpected light and he realized that hope for the future still remained.

"Well, uh, thanks, but it's definitely too early to know how many people are really immune—or if immunity is really possible. Josh says I'm not allowed to test that theory."

At the mention of Doctor Motorcycle Boy, Castle's chest deflated slightly. Oh. Right. Him. "He's the one that told you about the ninety percent fatality rate?"

Kate nodded. "That's what he believes he's seeing at the hospital. That was, gosh, five days ago, I think?" She shook her head and skimmed her fingertips over her forehead. "He's basically been working non-stop as you can imagine so we haven't really been able to talk."

"Sure. Makes sense."

They sat silently for another minute before Kate skimmed her hand down his arm and gave his fingers a squeeze. "Well, I'm really glad you stopped by to see us, but I should get back to this case—we're pretty shorthanded now that—well, now that over a third of the force is gone."

He sniffed and blotted under his nose with another napkin. "Right of course; I don't want to interrupt you."

She gazed at him, bemused. "Really, Caste? You don't want to interrupt me? Since when?"

Despite himself, he let out a breathy laugh; well she did have him there. "Well, I mean…I don't know what I mean. Sorry." He sighed and dropped his chin to his chest. As much as he wanted things to return to normal, he knew that his normal—sitting in the chair beside Beckett's desk and annoying her even though they both knew she wasn't actually annoyed—would never be normal again. His heart simply wasn't in it, not at that point in the grieving process, anyway.

He was surprised when a moment later he felt her fingers brush across his shoulders and momentarily feather into the hair at the base of his neck. "It's okay, Castle; don't worry about it. You can just…sit by my desk if you want. We don't have to talk."

He lifted his chin and saw she wore an encouraging smile, so what choice did he have but to agree? "Thanks, Beckett; that sounds nice."

* * *

Two weeks after his first reappearance at the precinct, Castle sat on the couch, his laptop balanced on his thighs as he tapped away, filling a blank Word document with a scene he'd thought of on the way home from the Twelfth. It wasn't one cohesive with the Nikki and Rook story he was presently writing, but he just hadn't found his footing there—not since everything happened. He struggled enough to write more than a few hundred words at a time that he knew he needed a longer break before trying to formulate a more organized story. For then, he'd be happy with just a scene that actually made sense even if it didn't fit anywhere and was ultimately scrapped.

The more time progressed, the more the world began to reset itself, the more Castle found himself settling into his new version of normal. True, the loft still felt almost painfully empty at times, and at least once a day he was convinced he heard either his mother or his daughter moving on the second floor, but living day to day was getting easier, slowly but surely.

After his first visit back, Castle returned to the Twelfth to visit with his friends and help where he could. There weren't many homicide cases to investigate (mercifully, the shock of the woman-murdering virus had calmed everyone's murderous tendencies—at least temporarily) but Beckett and her team had been tasked to other crimes, like a store robbery and a fire that turned out to be arson.

Very shortly after he, quite thankfully, discovered she was still alive, Kate was finally allowed to leave the precinct after her immunity to the mysterious virus had been confirmed by a blood test. She was, of course, very relieved to be back in her apartment and Castle couldn't say that he blamed her, but he was concerned. When he walked with her to the robbery scene the looks she received from men on the street were downright disturbing. They looked at her like…well, like she was the last woman left on Earth—except worse. They looked at her like she was a big juicy steak and they were starving stray dogs that hadn't eaten in weeks.

Castle knew better than to bring it up. He didn't want to upset her and knew she would respond only with, "I have a gun, Castle; I'm fine," but as the days progressed and the remaining women came out of hiding, reports of assaults and violence began filtering in. As a man who loved women with everything he had, he found the news utterly repugnant, but also knew he could not control the world (sadly) and so his concern for Kate grew, though he had to keep it to himself.

Just as he was contemplating which take-out location he would call for his dinner, the phone resting on the coffee table beside him rang and the lovely detectives imagine appeared on the screen. He smiled, swiped the device's screen to answer the call, and pressed it to his ear. "Beckett…you wouldn't want to share some Chinese with me this evening, would you?"

"Castle."

One word from her was all it took to send his heartrate skyrocketing, he sat up so quickly that his laptop nearly crashed to the floor; he caught it at the last second and shoved it to the coffee table. Pressing the phone almost painfully tight against his ear, he said, "Kate? Is something wrong?"

"I'm sorry to bother you."

"You're never a bother, Beckett. What is it?"

"Could…could you maybe come over to my apartment? Please. If you're not-"

"I'm leaving now," he said, before scrambling from the couch, nearly sliding across the hardwood floor in his haste to retrieve his shoes.

The writer made it to his partner's apartment in record time. (One good thing about their near apocalypse was that the significant drop in Manhattan's population had done wonders for the traffic.) When he found the ME's van parked out front, his chest was gripped with fear and he'd hurried inside past the uniforms guarding the building's entrance. He nearly ran smack into Perlmutter in the lobby, but was, perhaps most alarmingly, not met with the usual amount of sass, merely a terse head nod as he rushed towards the door.

Desperately concerned, Castle went for the elevator, but found it cordoned off with police tape. Cursing beneath his breath, he hurried to the stairs and took them two at a time for the first floor up, but then found himself winded and could only half-jog up the second flight until he reached the hallway outside his partner's apartment. He called out her name, but found her hovering in the doorway of her place, pressing a tea-towel covered bag of ice to her cheekbone already showing the shadow of a bruise.

"Oh god, Beckett!" he proclaimed, his stomach immediately flipping when he saw the cut on her lip and the ruffled nature of her hair. "What happened?"

Her bottom lip began to tremble and she merely shook her head, unable to get the words out. He hooked his right arm around her shoulders, pulling her into him and pressing his lips to the top of her head, quietly promising everything would be ok. After several moments she pulled back and confessed, "I killed him."

He skimmed his finger against her forehead to brush some wayward hairs from her eyes as he asked, "Who? Who did you kill?"

"He—he followed me into the building. I had headphones on…so stupid."

"No, no." He promised, but his heart clenched. God, oh god—his worst fear had come true. Some horrible, disgusting man had seen Beckett and—Jesus, he couldn't even bear the thought.

"He grabbed me by the hair and pushed me into the elevator. His hands were on my throat—I couldn't—couldn't breathe and my gun I…I—I didn't mean to k-kill him." She sniffled and rubbed her left hand beneath her nose.

Castle pulled her into his arms again while shooting a scathing look towards the elevator. "It's okay, Kate. You did what you had to do; you didn't have a choice."

"I-I tried to save him, but there was s-so much blood."

He brushed his lips over her head and cradled her against him even more. God, how horrible. She had taken lives before, of course, but always when she was on duty—always when she had no other option. Obviously, Kate had feared for her life and safety and thus used the only weapon at her disposal. Whether the man had intended to end her life or assault her in some other way (god, he couldn't even bear the thought) she had defended herself accordingly in his eyes and he could only hope the NYPD agreed.

After she'd cried against his chest for several minutes, she slid back and Castle brushed some tears from the bottom edge of her jaw. "Listen, I'm going to stay here with you tonight and then…I know you're not going to like this idea, but maybe you should stay at the loft for a while. Just until-"

"Okay."

"O-oh okay—okay." He stammered out his response. He honestly had expected her to protest and that he'd need to twist her arm into the idea, but he wasn't going to complain that she'd agreed so quickly. It really was for the best. He feared the situation in the city would get worse before it got better, and he if casually shadowed her under the guise of them living together then perhaps she would be less of a target.

After depositing her packet of mostly-melted ice onto the kitchen counter, she returned to his side and leaned her un-damaged cheek against his shoulder. "Thanks for coming, Castle."

He looped his arm around her back. "Always."

* * *

 **A/N** : Because I've been doing a lot of alternate endings and I can't help myself, there will be 2 independent "part 2"s to this fic, both branching off from this point.

* * *

 **A/N 2:** A bit longer explanation for this bizarre AU - feel free to ignore.

So actually i found this prompt on a non-fandom related fiction site like 10 yrs ago - the "mysterious virus kills 90% of one gender" prompt - and it stuck with me because I always thought it was interesting, if not completely bizarre and so for years I've been kicking it around, trying to figure out how to make it work semi realistically and this is the result so i hope you enjoyed this admittedly very strange AU.


	2. Ending 1

Castle sat casually in his usual chair, his left ankle balanced atop his right knee as he leaned one elbow on Beckett's desk and scrolled through his email inbox on his phone. They had just wrapped up a homicide case that had a motive that was disappointingly becoming commonplace: two men fighting over one woman—one of the few women of legal age remaining in the city. Another such woman sat just three feet from him and he could not have been happier for it.

Three weeks had passed since Kate moved into the loft and in Castle's mind things could not have been going better. Well, yes, they could have been if she had moved into his bedroom and not the upstairs guest room, but baby steps—he was confident they would get there. Otherwise, it was great. In addition to spending some of their days together they spent most evenings together as well. They shared meal-making duties (he was delighted to learn how good a chef she was when she took the time and didn't just settle for ordering takeout), ate together, and usually shared the couch in the evening as well, even if they were just reading quietly.

In exchange for living with him, Kate insisted on sharing some of the household duties even though the writer promised she didn't have to. This had led to some small annoyances between them as they became used to cohabitating with one another, but other than that their union had been going quite smoothly which, naturally, he was thrilled for. In Castle's mind there was nothing better than spending time with Kate Beckett and the fact that she could be there for him while he was slowly recovering from the heartbreak of losing his mother and daughter was merely an added bonus.

That particularly afternoon he was waiting for her to finish up her paperwork so they could go out to dinner together. She told him he didn't have to wait, but he didn't find it practical to go all the way back to the loft when the restaurant they wanted to go to was much closer to the precinct. Plus, he just liked being around her—he always had, but especially after everything that happened; he didn't worry about her when he was beside her.

Nearly two months had passed since the onset of the virus that had ended the lives of a staggering seven and a half million women and slowly more and more information was being given to the public. It had been determined that the airborne illness had been spread through the ventilation in the subway systems in each major city. Also, the initial estimates of eighty-to-ninety percent fatality rates for those stricken ill seemed to be accurate. As a whole, the country had lost nearly five percent of their female population. That was perhaps not the most staggering figure over all—and certainly not an unrecoverable number—however, in New York—far and above the hardest hit location—the absence was palpable.

Once it had been determined the virus was no longer active and it was safe for women to travel in the city, marketing campaigns were immediately launched to draw women to the city, though Castle imagined it would take several months for them to work; the fear was still too strong, no matter what the CDC said. Of course, within New York itself it was clear that men were already panicking that they would not be able to find significant others. Every time Castle heard someone call into a radio or read an online article he couldn't help but roll his eyes. Many of them had just experienced the death of their wife or girlfriend—didn't they want to grieve before worrying about finding another? Then again, as one of his poker buddies pointed out during their first game post-outbreak, he wasn't concerned because he had one of the half million women still alive living in his apartment. Castle could not argue with that point.

Still, their situation was complicated (when wasn't it?). He had asked her to live with him not for romantic reasons, but merely so that she would feel safe and not threatened despite the gun she wore on her hip. He hadn't thought of them in a more romantic aspect while setting her up in the guest room—at least, no more than usual. She technically had a boyfriend and he would respect that until she indicated otherwise.

"For you, detective."

"Oh, um, thanks. Just put it there."

Castle looked up from his phone when a box landed by his foot with a thud. He gazed down into the medium-sized cardboard container and found it full of dozens of letters and packages. His eyes skimmed over those at the top of the pile and he found they were all addressed to her—Detective Kate Beckett—care of the Twelfth Precinct. Intriguing.

"Fan mail?" He gazed at her, joking, but when she looked away solemnly he realized she saw no humor in his comment. "Seriously? I…I thought all the Nikki Heat stuff was filtered through Black Pawn." He reached into the box and picked up one of the regular-sized white envelopes to examine it. The return address stated that it was from Texas.

"'s not Nikki Heat fan mail." She mumbled to him.

"Then what kind of fan mail is it?"

"Here." She said, her tone indicating utmost impatience.

His brow wrinkling, Castle gazed up and saw that she gestured towards her computer screen where a rudimental website was displayed. The header read, "Find Your Apocalypse Bride!"

"What…."

"It's printing the names and addresses of women in New York who survived the virus." Kate closed the window with a rather violent click of her mouse. "Tech's trying to look into it, but whoever created it is pretty good at hiding their tracks. They try to take it down; it shows back up again. They're trying to get the FBI involved, but they're a little busy right now trying to find the sons of bitches who started this whole thing in the first place."

"Wha…" Castle gazed down at the letter in his lap. Had it been from a more local location it might have made more sense when combined with the website, but from so far away? That was baffling. He bent over and scooped up two more letters, one from upstate New York and the other from Jersey, which felt more in line with their conversation, but it was still so strange. "So these are from men who…"

"Apparently."

"May I?"

She flippantly waved her hand at him which he interpreted as approval to open the letters. He chose the Texas one first and skimmed through the page where, as Kate predicted, a marriage proposal existed—as unbelievable as that seemed. "Texas didn't even get the virus!" The writer muttered before opening another envelope and another to find letters that contained many of the same professions of love the only difference being that the New Jersey letter also contained risqué photographs of the sender—of course.

"Oh my god…are these all marriage proposals?"

"Some of them. Others are, ah, more explicit."

Though she'd mumbled the words her comment only encouraged him to dig further into the pile. Two letters later he'd uncovered what he'd both hoped for and dreaded: fully nude images and a letter that promised the sender to be a sexual rock star— _very_ explicitly. "Oh but Kate—he'll give you orgasms for days." The writer teased the detective, quoting directly from the letter.

 **"** Not funny, Castle."

He gazed down at the description which, at best, was copied from a grocery store romance novel. "It is a little bit."

She whipped her head towards him and slammed one palm down against the desk. "No, it's not—you would not think it's funny if you were me."

Castle pressed his lips tightly together and tucked Steven's nudes back into the envelope before she could see them. She was right—he knew that. If their positions were reversed he would have been horrified. Hell, he had been horrified three days earlier when they were walking home from the drug store and were approached by a drunken man aiming to proposition Beckett. He'd gotten in between them and the asshole had the nerve to slug him. Fortunately, in the man's inebriated state the punch was easy to duck, but it was enough to rattle them both. Though that was their only physical altercation, she had received at least several leering looks each day, and that was perhaps the saddest part of all.

"You're right; I'm sorry."

She offered a small smile before turning back to her arrest report. "Thank you. Now just…throw those back in the box so I can put them all in the dumpster before we leave."

"Really? You don't even want to look at a few of them? I'll even screen them for nudes if you want."

She gave him a bizarre look before saying. "No."

"C'mon—just a few."

She rolled her eyes. "You can look at them if you want, Castle but I—wait." She put her pen down again and gazed at him suspiciously. "You're not trying to get me to look at the box because you slipped your business card in there, are you?"

He gave her a pointed look, almost insulted at the accusation. "Of course not. I know you well enough not to do that—even as a joke. You don't want this." He tossed the letters in his hands back down into the box. "Professions of love and devotion from men you've never met? Men who promise all the diamonds and Prada purses your heart desires? Even if they weren't bullshit you still wouldn't want them. Material things could never win your heart. Friendship, trust, loyalty—things that are built over years, not five minutes of desperation. You want that one man who will be by your side no matter what—no questions asked, and you won't find that in a letter and certainly not in an amateur pornographic photo."

He watched her steadily for a moment as he sucked in a breath, not quite sure he'd meant to reveal all he had, but not wanting to take it back all the same. Her honey-brown eyes were perhaps open a bit wider than normal, but did not reflect anxiety or the desire to flee, merely curiosity. Glad he hadn't upset her, Castle skimmed his fingers along the edge of his chin and added, "Besides, I know something they don't: you have a boyfriend."

"No, I don't."

The writer nearly choked. "You—what?"

She turned her entire body towards him and rested her right elbow against the desk, lacing her hands together. "I broke up with Josh over a month ago; I thought you knew."

"I…I mean…" Wait, did he know that? How would he have known that? Oh, well, there was the fact that she called _him_ when she was assaulted in her apartment elevator—not the doctor whom he thought was her boyfriend. And she was living with him, which could have been innocent cohabitation, except—shit—they had spent all but two nights of the prior two weeks together in his apartment and he knew for certain that she was with Lanie both times she wasn't with him. Damn for someone normally proud of his observational skills he had failed miserably in this instance, hadn't he?

"I, um, I'm sorry to hear that."

She half laughed. "Are you really?"

"Wha—uh." He stammered, unable to form a full word. God, the way she was looking at him with that teasing smile—what was happening?!

After gazing at him for a few extra moments she casually turned back to her computer screen. "Don't worry about it, Castle; it wasn't right between us and hadn't been for quite some time. I don't know that it ever was."

She sighed, tapped out a few words on her computer, and then stopped. She pulled her hands off the keyboard and looked over at him with a small smile. "You're right, you know; you know me better than anyone, so why don't you take that stuff to the dumpster and by the time you get back I'll have this report done and we can go to dinner. If you don't mind?"

"Oh—uh yeah; okay Beckett. No problem."

He stood from his chair, pocketed his phone, and then hoisted the box from the floor. She gave him a nod and then turned back to her computer screen as he walked away rather dumbfounded, still trying to process the conversation they'd just had. The glimmer of hope that had always flickered within him was suddenly ablaze more strongly than ever before. Kate was single, unattached, and had just instructed him to dispose of what he could only assume to be around one hundred marriage proposals. From the way she spoke to him she implied that—oh god, could it be happening? Was it really their time? Maybe not quite yet, and that was okay given how raw his heart still felt, but it sure felt like they were heading in that direction and he could not have been more thrilled about it.

* * *

Glass of wine in hand, Castle walked from the kitchen to the couch but paused before taking a seat. His roommate sat with her legs folded, base of her wine glass resting against her right ankle bone. With her hair piled on top of her head in a messy bun he was able to see her face, and it seemed as though she was staring down into the goblet hoping the maroon liquid would give her answers to all the questions in the universe.

"You okay?" he asked as he sat down a cushion away from her, sitting sideways so he could face her.

She lifted her head and nodded. "Yeah I just…having a sad day I guess. Seeing that man break down over his wife and thinking about everyone who's gone…"

He hummed, took a sip of his wine, and then placed the glass on the table behind the couch. "I know; some days are harder than others." He could understand why the man's tragic tale had affected her so; it had upset him as well. His wife, like so many others, had died of the virus, but his daughter had survived only to be killed by a taxi driver who had jumped the sidewalk while texting on his cell phone. The situation was truly one of those moments when life wasn't fair.

"Sometimes I wish I had a job where only happy things happened."

He let out a breathy laugh, for such a comment seemed unexpected from her. "What? Like being a clown?"

She scrunched her nose. "Clowns are creepy."

"Then what?"

"I dunno. Just something." With that, she placed her wine glass on the coffee table and slid closer to him, resting her head against his shoulder and looping both her arms around one of his.

Castle gazed down at her in a mild state of shock. Was she really—had she just _cuddled_ with him? He wasn't complaining—not at all! If anything he was thrilled and in his elated state he could not help but wonder if it was finally happening between them.

For the prior two weeks, ever since he dumped her fan mail into the trash, things had certainly shifted between them. They ate almost all their breakfasts and dinners together unless she had a shift, and even then he tried to join her and the boys at the precinct. On the evenings she wasn't working, they tended to end the night as they were doing in that moment, with a shared glass of wine on the couch, talking about their day. It felt like they were a couple—except for the physical intimacy, of course—but even without that Castle still loved what they were becoming. Their relationship was blossoming into the thing he always knew they could become: something extraordinary.

Not wanting to ruin their moment, Castle merely turned on the television to the channel on which the Mets game was playing. He propped his feet up on the coffee table and relaxed back against the couch, the remote resting loosely on his lap. Kate responded by shifting closer to him and holding a bit tighter to his arm, which made the writer glad she couldn't see his face and the dorky grin that was spread across it.

An hour later, their team was down by seven runs and the game was becoming more depressing than entertaining, which meant that Castle had a predicament. He didn't want to continue watching the game that would surely end in a loss, but he also did not want to move as he was quite happy with the detective snuggled against him. With her body pressed against him, he never wanted to move—actually never. Like, for the rest of his life, which gave him a dangerous yet potentially brilliant idea.

"Well, I guess I'm done watching the Mets lose so, um, you want to go to bed?"

"Okay." She hummed, her voice already sounding a bit sluggish with sleep. "Another minute and I'll get up…"

"Actually." The writer continued as a few droplets of nervous sweat formed on his brow. "I meant: do you want to come to bed with me?" The detective slowly slid away from him enough so that she could tilt her chin and gaze up with a curious eye. Trying to make a joke out of his suggestion to lessen the way his heart was thundering, he added, "I mean so we can keep cuddling or whatever…" Then he winced at how dumb he sounded. Fortunately, Kate seemed more amused than anything else.

"Cuddling or whatever?" she echoed.

"Um, yeah I mean, ah…."

"Okay, Castle; just let me change."

"Wha…okay…" He agreed as she scooped up her wine glass. He then watched as she took it to the kitchen, placed it in the sink, and then ascended the stairs where she would presumably change into pajamas before returning to his bed— _his bed!_ Holy shit, this was happening…

…and he wasn't even remotely prepared.

After spending a few more minutes in the bathroom than he normally would, staring into the mirror and coaching himself that he was a forty-one-year-old man and of course he could share a bed with Beckett without wanting to rid them both of all their clothing in three-point-seven seconds, Castle opened the door and found the detective seated on the end of his bed wearing an NYPD t-shirt and black leggings, looking as positively breathtaking as ever.

"You, um." He cleared his throat as he walked into the room and hovered at the end of the bed. "You think you want an extra blanket or anything?"

She shook her head. "No I'll be fine."

"Okay. Well, um, you can have that side." He gestured to the one closer to the bathroom and then walked around to his usual side to take off his watch and peel back the sheet and duvet. Just as he sat down on the edge of the mattress he heard her say his name. Turning his head, he found her in a similar position, kneeling in the V-shape she'd created by pulling the blankets away from the pillows. "Yeah?"

"I just wanted to thank you for being patient with me," she said, sitting back against her heels. She folded her hands together and rested them against her thighs. "You've been very, very patient."

He wasn't exactly sure to what she was referring, but since it could have been any number of a few scenarios, he merely shrugged and promised, "I am a pretty patient guy."

She lifted her head and shook it as she tugged at her bottom lip with her teeth. "It's just so…ridiculous. We talk about everything, right? Except us. Except the thing that's probably the most important thing between us…right? Why is that?"

"Ah…wow, um…" He sighed as he sat down on the bed and thought about her question. They didn't talk about them—not really. He knew the reason he kept the subject off-limits: because he knew her and her closed-off heart and was too terrified that blurting out how he truly felt would scare her away forever. Not wanting to say exactly that (for fear of scaring her away forever) he gave a subtler answer. "I guess the fear of upsetting the status quo. Maybe?" He certainly felt happier being just her partner than not being in her life at all and suspected the feeling might be mutual.

"Even after everything that's happened? Millions of women are dead; the world will never be the same so something as simple as saying, 'I want to be with you,' should be easy." She sucked in a breath and gazed at him, but his expression didn't falter despite the way his heart had begun thundering as though he was outrunning a bear. She sat up a bit straighter, set her shoulders, and continued. "So there it is. I want to be with you; I'm ready."

"I was born ready—I mean—shit." He cursed the moment he heard how stupid his comment sounded in such a tender moment. "I'm sorry—I shouldn't have said it that way."

Despite what he assumed to be a mortified expression on his own face—or perhaps because of it—Kate laughed. "No, its fine it's—it's why I love you."

When those three key words hit his ears the writer nearly collapsed on the mattress. Had she really intended to say them? To reveal something he wouldn't have expected from her even after months of dating? "I…you…"

Her cheeks burned red and she tucked an escaped strand of hair back behind one ear. "Sorry, I, uh, hope that wasn't too soon."

"T-too so—No! No—are you kidding me?" He thrust his arms forward and gripped onto her shoulders, joy positively exploding across every inch of his face. "I'm so in love with you." He was and had been for the better part of a year; she was, without question, the most amazing person he had ever met and she brought him more joy than he ever thought possible.

She smiled, brought her hands up to rest on his elbows and scooted a bit closer to him. "I…I realized when we were in LA, but it scared me and then this virus happened and if I had been sick without you knowing how I really felt…" She shook her head almost remorseful. "I don't want to be afraid anymore."

"Kate." He sighed out her name like it was the answer to the prayer he'd been waiting for his entire life. Unable to resist a moment longer, he slid forward and pressed his lips against hers. He soon felt her hands against his cheeks as she leaned deeper into the kiss, humming out his name when their lips separated.

Gazing at him with a level of devotion that made his ribs feel as though they'd crush his swelling heart, she said, "I never thought I'd find someone like you, but I'm so glad that I did."

"Me too."

Castle gathered her up in his arms, kissing her with a years' worth of pent up passion. Soon they had fallen back against the mattress and her hands began roaming his back and creeping beneath his shirt. Her fingertips were cool against his skin but he almost welcomed the contrast in temperature. When he moved his lips to her neck and she giggled out his first name, the writer felt an electrical impulse down his spine, shocking him back to reality.

The virus. So much had changed. So many women had died—his mother and daughter among them. Yet, there he was, the woman of his dreams in his arms and he was about to make love to her. He was about to become happier than he'd ever been, but yet still so many suffered, so he shut his eyes, rested his lips against her collar bone, and uttered a silent thank you to the powers of the universe that had given him that moment.

"Are you okay, Castle?" she asked, her hands skimming against his ribs.

The writer lifted his head and gazed down at his companion, nestled in his arms against the pillows on his bed. Her lips were pink and slightly swollen from their kissing, her bun was beginning to fall out causing hair to cascade down around her face, and her eyes were sparkling with excitement. She had never looked more beautiful. "Yeah—I. Yeah." He responded, his voice husky with emotion. "You're perfect."

She flushed and looked away from him, refusing the compliment. "Oh god no; the furthest thing from it."

Brushing his lips against her cheek, he nuzzled his nose into her hair and whispered. "You're perfect for me."

* * *

 **A/N** : Hope you enjoyed "ending 1" - the second ending will be coming in a few days!


	3. Ending 2

**A/N:** This ending is 100% independent of the previous one and picks up after part 1

* * *

Still drying his damp hands on his jeans, Castle returned to his unofficial seat in the twelfth precinct beside his partner's desk. Unlike several minutes earlier, she was not seated at the desk, but he didn't think much of it; she may have been grabbing a file or something off the printer. He would have simply sat and not given it a second thought at all except for the fact that from the corner of his eye he spotted Ryan and Esposito clustered oddly close together as they stared towards the breakroom.

A curious man by nature, he could not let this slide, so he approached from behind and asked, "Whatcha doin'?"

Esposito turned and looked at him as though he'd been on vacation for a month. "Where have you been?"

"I was on the way to the bathroom when I bumped into LT; we were talking. I was only gone like five or six minutes."

"Well, you missed this." The detective said, nodding his head towards the break room.

Looking between the men, Castle could just barely see through the window in the breakroom a man in a dark suit and dark tie that simply screamed "Fed" just by the looks of him. Though she was barely visible, he could see the top of Beckett's head as she faced the man and deduced they were having a serious conversation.

"Who's he?"

"No idea." Ryan replied. "He came off the elevator, went directly to Beckett's desk, flashed a badge, and they've been in there ever since. He seems kind of…"

"…spooky." Espo concluded.

"Well maybe he's a Spook." Castle concluded. If that was the case, the explanation seemed obvious. "Beckett was immune to that virus. Maybe it has to do with that."

"Can't imagine she'll like that very much," Ryan concluded.

The writer pressed his lips tightly together, silently agreeing. Just over three weeks had passed since they moved in together and things were going well for them. Their transition from partners to roommates had been so smooth it merely solidified in his mind that they would one day become a couple, but he was patient. His heart was still recovering from the loss of the other two most important women in his life, so he wasn't in any rush to pursue Kate romantically, especially since her relationship status seemed to be in limbo at the moment. He was simply glad for the elevated level in their friendship. Plus, he was happy to be there for her when she needed someone to talk to.

For the first few days after she moved in, Kate didn't say much. She kept mostly to the guest room and seemed to be avoiding him at mealtimes when he was in the kitchen. Just as he was beginning to wonder if she regretted accepting his invite, she came to him and apologized for her standoffishness and confessed that she had been unexpectedly upset by her assault, as it reminded her of the thing she was trying not to think about: just how few women were left in the city.

That evening they talked about it, and he could tell how much she struggled with not just being a survivor, but being completely immune. Apparently, in her opinion, the man had not attacked her with the intent to sexually assault her, but because he was furious that the women in his life had died while she remained alive. While he could not promise her that no men thought that way, he did assure her that those that cared about her—himself, her partners, and many of their coworkers at the twelfth—could not have been happier she was alive and certainly wished her no ill-will. He also told her not to rush through her feelings, for the survivors guilt she was feeling was just as valid an emotion as the grief he and many others felt.

In the weeks that passed since that event, she seemed to be doing better, but Castle feared that the federal government seeking her out for any reason would set her back. Not that he could blame her; he wouldn't want to be used as a pin cushion—particularly not over something completely beyond his scope of control.

For the next several minutes, the trio of men stared into the breakroom as though it was the opening scene in Broadway's most anticipated show of the year. Only when the female detective and her Fed companion pushed themselves into standing positions did they scatter back to their respective seats and attempt to make it seem as though they had never been spying at all. Castle rested his elbow against Beckett's desk and pretended to rest his cheek against his fist as he looked as his phone, but really he gazed at the breakroom exit from beneath his brow line. He took note of the fact that the detective exited the room briskly and did not appear to say a formal goodbye to the suit-wearing man now making his way towards the elevators.

When his partner returned to her seat, she did not look upset or irritated, but actually rather ill. Her skin was paler and her fingers appeared to be trembling, which had him concerned greatly for what the mysterious man had asked of her. "You okay, Beckett?"

She gripped onto the arm rests on her chair, looked over at him and said, "I don't know."

His level of concern immediately doubled. If she was not even going to attempt to brush off her feelings as nothing or deflect by saying they would speak about it later, something truly upsetting must have taken place. He leaned in closer to her and lowered his voice. "What's going on? Who was that man?"

"Ah…" She hedged and flicked her eyes past him to gaze at the other two members of their quartet, who presumably were failing at the task of pretending to look busy while actually eavesdropping intently on their conversation. "It's—it's nothing. Really. I, um, I think I'm actually going to go for a walk to clear my head."

His brow knitted. "You…want company?"

She shook her head. "No, no; you stay here and see if you can help the boys ID who was in that security camera footage; I'll talk to you later."

"O-okay, Beckett; as long as you're sure."

She managed to give him a half smile though he was not at all reassured by it. Instead, he watched her walk towards the elevator until she stepped into the car at which point he turned back to gaze at the boys and give them a shrug. Something was indeed going on and he most definitely would be concerned about it until she revealed the truth to him, which hopefully would be sooner than later.

* * *

Several hours later Castle returned to the loft more concerned about his partner than ever. She had not returned to the Twelfth but instead texted Esposito to tell him she was going home for the day, and was only to be interrupted for something critical with regards to the case. Castle had put in an extra hour at the Twelfth helping the boys, but then left once his distraction over what was going on with his partner overtook his ability to focus on the case.

Stepping inside, he spotted her immediately, curled up on the corner of the couch cradling a mug of tea in her lap. He didn't say a word; he just walked over and sat down beside her. She glanced over at him and reached forward to place the empty tea mug on the coffee table and then sat back against the couch with her hands folded in her lap. When the silence in the room persisted beyond the two minute mark, the writer could stand it no longer and encouraged, "Beckett please; talk to me."

Her gaze remained on her lap as she said, "That man I met with today—Branson—he's from the federal government—part of the new task force they've formed with regards to this whole…incident."

"The virus?"

She nodded and looked up. "Yes, but more the aftermath. He came to inform me of a new initiative the government is setting forth—particularly for women like me; ones who are immune."

His brow wrinkled. "How did they find out about your immunity?"

She shrugged. "That lab Josh sent my blood sample to must have kept records or maybe it was a government lab—who even knows. The point is: the initiative is for these remaining women to become pregnant—as quickly as possible."

"O-oh." The writer swallowed hard as he processed her words. Had the virus affected the entire country, he would have understood such an immediate push. The female population of the United States dropping by almost ninety percent in a few week period? Yeah, that would be, as he'd heard suggested on the news, an extinction-level event, but that was not the case. Only the women in a handful of major cities had died, dropping the country's female population by around five percent. While this was not something to be ignored or taken lightly, in his mind it hardly warranted such a dramatic reaction.

Kate unfolded her legs and scooted towards him on the couch, reaching out both her hands to rest on his forearm. She gazed at him with wide-eyes. "It was so…god, Castle." She dropped her chin to her chest and shook her head, taking a few deep breaths.

Hearing the desperation in her voice unsettled him, so he asked, "What is it?"

Her head still shaking, she lifted it once more. "The way he spoke—it was like I didn't have a choice."

Despite the fact that his partner appeared visibly distraught, Castle almost laughed. "What do you mean? This is America; of course you have a choice."

She pushed herself away from him and stood. Walking around to the opposite side of the coffee table, she hugged her elbows and kept her arms tightly against her chest. "I don't know, Castle; I really don't. He…he talked about this campaign they were going to set out for all women, but particularly those that had survived or been immune to the virus. He said it was my duty as a civil servant to participate and become, god, Castle—it was like he wanted me to be some sort of poster child for this program."

"Kate." He began, his voice as steady as ever as he stood and approached her. "If you don't want to have children, you don't have to have them; no one can make that decision for you."

She shook her head. "You weren't there; you didn't hear him, Castle. He said all these things and I-"

"Hey, c'mere." He reached out a hand and grazed his fingers down the back of her arm, carefully leading her back towards the couch. He could see how upset she was becoming and he didn't want her stressing over something he just could not believe to be reality.

"It's not that I never wanted kids, you know?" she said as she sat down beside him once again. "I just never was in a relationship serious enough to really think about it and I…I never thought I'd have to have them like this…I never thought the world would be like this."

"None of us did." He added softly as the faces of his mother and daughter flashed through his mind's eye.

She sighed audibly and leaned her body against his so that her head fell against the top of his shoulder. He looped an arm around her back and grazed his fingers up and down her arm for several minutes, before an idea hit him. "Why don't you go and take a relaxing bath and I'll make us some dinner?"

"Oh, I…" She lifted her head and gazed at him hesitantly, her hands moving to cover her stomach. "I don't think I can eat anything."

"Well I'll make something light and you don't have to eat it if you don't want, but you might feel better after your bath. You can even use the master if you want—my tub has massaging jets." He added with an enticing eyebrow wiggle.

She let out a breathy noise that wasn't quite a laugh. "A regular tub will be fine, Castle; thanks."

* * *

Shortly after eleven p.m., wearing just his boxers and a t-shirt, Castle emerged from his bedroom to double-check that he had remembered to cover the dinner leftovers after placing them in the refrigerator to cool. Operating on auto-pilot, he crossed the hall, walked through the kitchen and opened the refrigerator only to discover two containers of uncovered food. He flicked on the overhead light, pulled the roll of cling wrap from the under-counter cabinet, covered the bowls, returned them to the fridge and had just turned around to reach out for the light when a figure hovering at the foot of the stairs startled him.

"Jeez, Beckett!"

"Sorry," she said meekly, retreating to the bottom step once more.

"'s fine; I just thought you went to bed." Or so she had told him a few hours earlier after only eating a small amount of the dinner he made—not that he minded. Given what she had told him, he did not blame her too much for having a limited appetite.

"Couldn't sleep. I just can't stop thinking about…about today."

He shut off the kitchen light and crossed over to turn on the one in the hall. Then, he stood by the stairs waiting for her to continue.

"You know what he said to me, Castle?" She skimmed her hand over the bottom of her chin, shaking her head with obvious irritation. "He asked me if I was in a serious relationship and when I said no he said, 'That's okay; we don't have any shortage of men.' Can you believe that?" She pushed herself into a standing position and threw her arms out to her sides. "Like I could just pick some guy at random to father my children; like it wouldn't even matter because all I needed was the sperm."

The writer hummed. "A little cold, I'll admit—but did you really expect much else from a Fed?"

She gave him a look that indicated she understood his point, but then bit down on her bottom lip with her teeth and folded her arms across her chest. "That's not—I wouldn't—I mean…" She shut her eyes and let out a breath, presumably collecting her thoughts. "If I do this, which, the more I think about it I'm not sure that I have a choice, but if I do this it couldn't be like that. I never wanted just a child, but a family. I don't just want any man; I need a partner—someone I choose, not one provided for me."

Castle sucked in a breath as he locked eyes with the detective and saw she appeared more determined than ever. God—oh god. Was this happening? Was it possible? Was their conversation leading the direction he thought it was? It seemed something too impossible to hope for, yet there she was standing before him, both of them in their pajamas, speaking about her feelings without hesitation, which had never happened before.

As his mind reviewed their situation, something she said moments earlier struck him and his brow wrinkled. "Wha…did you say you told that guy you weren't in a serious relationship?"

Her forehead also wrinkled. "I broke up with Josh weeks ago—I thought you knew that?"

He'd presumed it given her actions—and presence in his home—but never had official confirmation. "I…I wasn't sure."

She shrugged and scrubbed her big toe against the hardwood floor. "Not like it would matter; Josh wouldn't be the man to do this with. I couldn't depend on him to stay, commit, be the partner I need."

"Right, but-"

"The thing is." She interrupted him before raking her hands through her hair, spinning around on the spot and looking more rattled than before. "God—the thing is…The whole world has changed—all of it. This virus changed everything—including me. At least, I'm trying to change because I could have died. If I wasn't immune I would have died and then…then I would never have even had the chance to…" She squeezed her eyes shut and one tear fell down her cheek; Castle felt his breath catch in his chest at the sight of it, torn between observing her heart-stopping beauty from afar and gathering her up in his arms and promising everything would be okay.

She opened her eyes, took a tentative step in his direction and blurted out, "Will you do it?"

"Will…I…" He echoed, both confused and stunned by what was transpiring in his foyer.

"If the government is really forcing me to have a child will you—will you be the father?"

"I—yes." His mouth responded before his brain had fully processed the statement, but the rattled breath she took shocked him back to reality. Tears began spilling out of both eyes and she tucked her hair back behind her ears before lowering her chin. "Hey, hey." He stepped forward and put his hands on his shoulders. "Don't cry, Beckett; I said yes."

She let out a soft laugh as a mixture of relief and embarrassment crossed her face. "No, I know I just—I'm sorry."

"No need for an apology," he said. Then, without any effort, he pulled her towards him and wrapped his arms around her shoulders while hers slipped around his waist. Good god—what was happening? Had Beckett just asked him to father her children? That was certainly a zero-to-sixty escalation in their relationship that he was not expecting, but he wouldn't complain about it! She was entirely right in what she said; the world had changed and as such they didn't have time to waste dancing around their feelings. He loved her and was committed to the relationship they had in whatever form it took.

After a several minute hug she pulled back, brushed her fingers beneath her eyes and gazed up at him tentatively. "Are you sure about this?"

He bobbed his head. "I'm here for you, Beckett, in any way you need—partners, remember?"

She shook he head. "This is a completely different kind of partnership."

While technically true, he'd seen their partnership as much more for quite some time. "Still; I'm in."

She nodded and thanked him then added, "I'm still not sure about all this."

"I understand, but might I suggest sleeping on it? You might feel clearer about things in the morning. C'mon." He took a step towards his bedroom and gazed at her expectantly.

"O-oh—you mean your bed? Both of us?"

At her hesitance, he shrugged. "Why not? Besides, this way if you wake up in a few hours and are dying to talk more about this, I'll be right there. I'll hit you with a pillow, but I'll be right there."

She smiled and let him lead the way. "Thanks Castle."

* * *

Richard Castle opened his eyes the following morning to a far more attractive sight than the usual pile of tussled pillows beside him. Instead, he found a beautiful brown-haired woman curled up on her side with her hands tucked beneath her head. Even if her brow was wrinkled in deep thought, she was still the most gorgeous thing he'd ever woken up to in his life and considering his forty-some years on the planet: that was saying something.

"Hey." He managed through a yawn.

"Hey."

"Feeling better this morning."

She shrugged. "Not really."

He grunted and arched his back pressing his hands against the headboard as he stretched out. "You're not worried about all the medical stuff, are you? Because I'll go to any doctor appointment you want, Beckett. Even when they, you know, take your eggs out—assuming they let me. Or do they do that in an operating room?"

She blinked at him. "What?"

He mirrored her confusion. "Or, do they have to take the eggs? That's how they do IVF, right, but I guess sometimes they can just put the sperm-"

"What the hell are you talking about?"

His foggy brain attempted to adjust from being asleep to the conversation he was in the middle of. "Um…having a baby?"

"Yeah and you had one so how do you not know how this works?"

"Wha—no." He shook his head. "Meredith and I had Alexis naturally."

She sat up and moved towards the opposite edge of the bed. "And you don't want to do that with me. Then maybe-"

"Whoa—what? What are you talking about?"

"What are YOU talking about?" she responded.

"I don't know!" he truly did not. How did the most amazing morning of his life—the first waking up beside Kate Beckett—taken such a wrong turn at his hand? "You—you were talking about the Fed guying saying all you needed was sperm so I—I guess my head got stuck in this clinical place but no, I—I want to have a baby with you—the normal way; the sex way. I…sorry?" he offered with a grimace.

She sighed and flopped down against the pillows again. "God, Castle; don't scare me like that."

"No, no I'm sorry—I'm so sorry." He moved closer to her and skimmed his hand across her abdomen so he could hook her waist and use his hand to drag her closer, sliding her body across his silky sheets until they were side by side. "How could I not want to be with you?"

Without waiting for a response, Castle pressed his lips against hers, but only briefly. When he pulled back he saw that she wore an ever-widening smile, which made him grin. Her fingertips grazed against his forearm causing chills to form across his skin. He husked out her name and she hummed in response before he kissed her again, that time letting his body fall against hers as they melded into each other.

Several minutes later their heads had returned to their respective pillows thought their bodies were still close; his hand danced against the exposed skim at the top edge of her pants and her thumb brushed lazy line across his cheek. "Now that you've had a chance to think about it, are you still sure about this?" he asked her. Though he wasn't entirely sure if he wanted to hear the answer, it was the question he needed to ask before he fell any harder than he already had.

She smiled and nodded. "I knew from the moment we saw each other again—well before that, actually. I knew in LA, but I was scared of how I felt and then everything happened and…When I finally saw Josh again after almost two weeks apart it was just kind of like 'Hey, how are you?' No different than our normal greeting and I knew that whatever was left of our relationship was gone. But when I saw you? Rather, when I saw you see me it was like your world started spinning again and I realized that you probably-"

"I'm in love with you." He confessed without second thought. Normally, he would not have made such an admission—not to Kate Beckett who was, at the very least, skittish when it came to matters of the heart, but things had changed—after the virus, after she asked him to father her child, now that they had made out in his bed…

"I-"

Before Kate could get out more than one syllable, their moment was interrupted by someone pounding on the apartment door. No—not pounding. Pounding implied a human using their fist very sharply. This sounded more like a battering ram.

"What the hell?" Castle muttered, throwing back the covers on the bed and shuffling his way towards the foyer, where the racket continued. With his companion just a few steps behind him, they paused just outside the bedroom to listen to not just the banging, but what also sounded like clawing at the door handle and frame. The writer gazed back over his shoulder at his companion with a befuddled expression.

"Should I get my gun?" she whispered.

"They can't get through the door." He replied. He took two steps towards the door with the intent to look out the peep-hole but was stopped when Kate grabbed on to his arm.

"No; they could have a gun and shoot you through the door."

"If they had a gun, they'd be shooting, not banging." He rationalized.

"I can hear her! I can hear her! I know she's in there!"

The male voice on the other side of the door shouted in a manic way. The tone reminded Castle of the junkie they'd found hovering over a murder victim one time. Beckett and Esposito had tried to talk him down, but ultimately had to shoot him when he lunged at them with a weapon that turned out to be shards of glass from a broken bottle.

"I need to see her! I need her! Please! Please!"

Now thoroughly perplexed, Castle turned to look over his shoulder at the detective, who seemed more annoyed than anything else. "I thought this building was secure?"

"It is!" And damn well better have been for the fees he paid for living there.

Pressing her lips together, Kate stalked over to the door and gazed out the peep hole before walking over to the lockbox just inside the coat closet and retrieving her service piece. Returning to the door, she called out, "This is Kate Beckett of the NYPD; you have thirty seconds to vacate this hallway or you will be arrested for trespassing."

Unfortunately, this threat did nothing to deter the man. If anything, hearing her voice encouraged him, for the pounding and clawing continued at an even more frantic rate. "Let me in! Let me in! Let me see her! I need her!"

"Should we call someone?" Castle asked, hovering just a few feet behind her.

She sighed. "I'd rather not deal with the paperwork. C'mere—brace this door."

"Wha—what are you doing?" he asked with mild horror as she undid the locks. When she gave him a pointed look, he did as he was told and braced his body against the door while she opened it just wide enough to slip the barrel of her gun out. Fortunately, this added threat was enough to send the crazy man scurrying back towards the stairwell. Castle called down to the doorman on duty and made sure the man was escorted from the premise before turning back to his companion, who was once again securing her weapon.

"Do you think it's possible that just like one percent of women were immune from the virus, it made one percent of men go crazy?" the writer mused, taking into consideration that event and some of the other bizarre reports he'd heard on the news.

She sighed and leaned against the closed closet door. "I think I'd believe just about anything is possible at this point."

"REALLY!?"

"About this situation, Castle—I still don't believe Big Foot is real."

His chest deflated. "Don't tease me like that, Beckett."

"Sorry." She smiled, though briefly, for as she stepped towards him worry lines appeared on her brow once more. He stepped up beside her and skimmed his arm over her shoulders.

"Hey. We're going to get through this, you know. Crazy as it seems."

"Partners?"

"Always."

She stood up on her toes and kissed him before resting her hands in the center of his chest. "Castle, listen, about what you said before that maniac arrived. I…I'm not the type of person who can rush into relationships. Even with everything that's happened I can't change that part of me. I need time to adjust to all this, but I don't want you to think that I…that I haven't… you're extremely important to me."

"I understand and I'm not rushing. The federal government is rushing but I'm not."

She let out a mirthless laugh. "Thanks."

He grinned. "No problem." Then, after pressing his lips against her forehead, he stepped back and tugged her towards the kitchen. "C'mon; let me make you some of my world-famous pancakes for breakfast."

* * *

"Castle."

The writer's attention was pulled from his phone at the sound of the concern in Beckett's voice. He gazed up to meet her eyes and noticed her gesturing behind him, where he saw the same Federal representative that had been in the precinct two weeks earlier. "He's back."

"Yes."

Turning his eyes back to Kate, he snuck his hand across her desk and closed his fingers lightly around her wrist. "Whatever you need; I'm here."

She smiled at him. "I know."

In the two weeks since the Fed's visit had altered the course of their lives things had been going exceptionally well for them—far better than he'd ever expected. Unlike in the past when they were both guilty of not being honest about their true feelings, in light of the earth-shattering recent events they had adopted a fully-honest policy. For the several days after Kate's tearful request for him to father her child should the government require her to bear children, they spoke for several hours on the subject of them, their relationship, and their future. They talked about what their lives might look like if they jumped from being non-romantic right to starting a family, and how they felt about missing out on the middle stages of a relationship; those steps they would have taken had the world not taken a sharp left turn on its path through normalcy. In the end, they agreed to expedite the speed of their relationship if the government contacted Kate again. Now, it appeared, that was indeed what was taking place.

"Ms. Beckett," The fed, Branson, said when he approached her desk. "It's nice to see you again. May we, perhaps, have another few moments in private?"

"Only if my partner can join us," she said, glancing over her shoulder to Castle.

Branson looked at Castle down the bridge of his nose and then turned back to the detective. "If that's what you want."

The trio entered the breakroom and took a seat around the round table there. Castle sat immediately beside his partner and fought to resist the strong urge to take her hand during their chat.

"Have you had a chance to think about my request?"

Kate looked at Castle briefly before turning towards the man. "Yes, and I intend to accept—assuming I will have the freedom to get pregnant on my own timeline."

Branson blinked. "And what might that mean?"

"Well when you were here last you talked about encouraging women to become pregnant as soon as possible, but I was thinking more like…six months from now."

Though clearly irritated, the man said, "That seems reasonable. Now, when I was here last you said you did not have a father in mind. Would I be correct in assuming that circumstances have changed?" he asked with a notable gaze in Castle's direction.

"Yes. My partner will be the father of my child."

The Fed retrieved a notebook and pen from the breast pocket of his blazer. "Your name, sir?"

"Richard Castle."

The man wrote down the name and then put the notebook and pen back in their place. "Very well. We'll have you both brought in for your medical examinations in the next-"

"I'm sorry." Kate interrupted. "Medical examinations? You didn't say anything about those before."

The man shrugged. "They're quite routine, I assure you. Fertility and genetic screenings to ensure that your offspring are as healthy as they can be, all things considered. And if, for whatever reason, Mr. Castle is not suitable then-"

"I've had a child before, so I doubt that will be a problem." Castle snipped, fighting the urge to react more aggressively to the man's creepy business-like tone.

After giving an expression that indicated he was less than convinced, Branson bid them goodbye, leaving the partnered duo alone in the breakroom. "You're right," Castle said, "he's massively creepy."

She grimaced. "I know. It…it doesn't make you want to change your mind, does it?"

He twisted in his seat so that he could face her. "No. Not unless you're changing your mind. We're in this—partners, remember?"

She sighed and rested her forearms more heavily against the table. "And, if for some terrible reason, we're not genetically compatible?"

"Then we'll adopt. Or find a sperm donor that is compatible and that child will be ours."

"Really?"

He nodded without hesitation. Of course it would be disappointing not to have a child that was genetically both his and Kate's, but if for some reason they were unable, he would not be opposed to the ideas he suggested. Any child they brought up together would be theirs and it would be wonderful no matter how that child came about. "Really, Kate."

She reached out and cupped his face with her hands before whispering, "Thank you," and pressing their lips together.

Not a moment later their kiss was interrupted by an obnoxious throat clearing. The lip-locked duo turned their heads to find the remaining part of their quartet gazing at them with perplexed expressions from the breakroom door. "Um…are we interrupting something?" Ryan asked.

"No." Kate replied before standing and walking towards the coffee maker as casually as ever. Castle followed a few steps behind her.

During some of their discussions the subject of whether or not they would reveal their official couple status to their partners had come up. Since, at the time they had yet to even make love, they agreed they would keep the blossoming romance to themselves for a while longer. Even after they'd crossed the intimacy barrier they still hesitated to make an official announcement, but now that the federal government knew about it, it only seemed fair their partners did as well. On top of that, there was quite a bit more to explain.

"Nah—it's only the government forcing Kate to have a baby; no big deal."

"Castle…" she said in a tone that half scolded him and half sounded exasperated.

"What the—they can't do that!" Esposito proclaimed.

"You'd be surprised." The female detective commented.

"Is it because you're immune?" Ryan questioned. Kate nodded. "So…what are you going to do?"

Kate glanced at Castle and smiled. "Well, we talked about it and…yeah, we are." The writer stepped up beside her and looped his arm around her back so that it rested on her hip before gazing at the now wide-eyed male detectives.

"I see…"

"So does that mean you two are done making out?" Espo asked. "Because we have a case."

Castle grinned at Kate before looking at the boys. "Then lead the way."

* * *

"I've said it before and I'll say it again: you really did _not_ need those hormone shots they forced on you."

Castle sighed as he descended the stairs of the loft, baby monitor in hand. His wife gave him an expression that clearly said, "Tell me something I don't know," as they had been down that road _many_ times before in the prior eight months, ever since finding out Kate's womb had a double occupancy. Really, it was ridiculous—so her estrogen levels were on the lower end of the average spectrum—that did not mean a dramatic drop in fertility. Hell—they hadn't even tried and failed to get pregnant more than one month. He was shocked when she'd agreed to the shots and planned on never letting her forget it, either.

Kate placed the last rinsed out baby bottle on the dish rack to dry, and then turned to him while wiping her hands on a towel. "I thought you said having twins would be an adventure?"

"That was back when I was sleeping through the night."

"Castle," she said with a warning laugh.

He placed the baby monitor down on the edge of the kitchen counter and approached her with a knowing grin. He truly did love his children and, though it had barely been six weeks, he could not imagine his life without them, but having two babies was definitely more than double work compared to just having one. "I'm kidding—mostly. I wouldn't want to give up Cagney or Lacey."

Kate rolled her eyes and poked him in the chest. "Give it up, Castle; we're not changing their names."

He let out a tragic sigh, still slightly irritated she had instantly vetoed his very witty baby name suggestion. "Fine, but you know I think Avery smiled at me when I was putting her down."

"Did she?"

He hummed. "Jackson smiled too…but it was definitely gas."

"Just like his father."

"Yeah—hey!" He whined when her jab processed in his mind. When she smirked at him, he looped his arms around her waist and pulled her in for a kiss.

"C'mon Castle; we'd better get to bed since they'll be up again in…three to four hours."

She went to leave the kitchen, but he held her tight, gazing at her very seriously. "You know I wouldn't change a thing, right?"

Cupping his jaw, she nodded. "And neither would I."

* * *

 **A/N:** Thank you all so much for reading. Hope you enjoyed this strange little AU!

Up next is **A Different Kind of Magic** \- it will also be 3 parts


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